Cover plug of the core of a fast neutron nuclear reactor

Abstract

The cover plug (4) comprises a cylindrical barrel (8), a support plate (10), a group of vertical tubes (12) for the control rods and for the instrumentation of the core, an apertured transverse plate (28) fixed to the lower end of the barrel (8) and a transverse deflection plate (32) located above the apertured plate (28). The transverse deflection plate (32) is suspended from the barrel (8) by substantially vertical elastically yieldable strips (34) evenly spaced apart on the periphery of the barrel (8). The strips (34) are welded to the barrel (8) by their upper end and to the edge of the deflection plate (32) by their lower end. They are located in the region of openings (35) in the barrel (8) which permit radial movement of the deflection plate. The deflection plate (32) is also integral with tubes (14b) receiving the control rods disposed in a single row coaxial with the barrel (8).

What is claimed is: 
     
       1. In a fast neutron nuclear reactor having a vessel closed by a structure comprising a rotating plug, said vessel containing a core and a coolant liquid, said nuclear reactor having control rods for movement into and out of said core, a cover plug structure for fixing and guiding the control rods and instrumentation of the core and deflecting and dispersing the coolant liquid, said cover plug structure comprising a cylindrical barrel having a vertical axis, a support plate integral with an upper part of the barrel for bearing on a rotating plug closing the vessel of the reactor in which vessel the core is immersed in the coolant liquid, a group of vertical tubes at least a part of which tubes receive control rods of the reactor, fixed in an upper part of the tubes to the support plate and disposed inside the barrel in a plurality of rows coaxial with the barrel, an apertured transverse plate fixed to a lower end of the barrel and allowing passage of the coolant liquid and the vertical tubes the spacing of which it ensures, and at least one transverse plate for deflecting the coolant liquid on which plate are fixed vertical tubes of the group which serve to effect measurements in the core, said deflecting plate the diameter of which is less than the inner diameter of the barrel being located inside the barrel above the apertured plate, the improvement wherein, for suspending the transverse deflection plate from the barrel, substantially vertical elastically yieldable strips are evenly spaced apart on the periphery of the barrel and welded to the barrel by an upper end of the strips and welded to an edge of the deflection plate by a lower end of the strips, openings being provided in the barrel in regions of the respective strips, said openings having a shape corresponding to the shape of the strips but with a slightly smaller size to allow movement of the strips outwards into the openings and of the deflection plate radially of said vertical axis, the deflection plate being integral with some of the tubes which receive control rods and are disposed in a single row coaxial with the barrel, the tubes thus ensuring the support of the deflection plate.   
     
     
       2. The improvement according to claim 1, wherein the openings in the barrel are cut out substantially in a shape of an inverted T and the elastically yieldable strips have a substantially corresponding inverted T shape, a widened lower portion of the strips corresponding to the transverse part of the inverted T being bent at substantially 90° toward the interior of the barrel and welded to the edge of the deflection plate, and wherein the tubes which receive control rods and are integral with the deflection plate are disposed in a circular row coaxial with the barrel and have a radius which is between one-third and one-half of the radius of the barrel. 
     
     
       3. The improvement according to claim 1, wherein the openings in the barrel have an upper part substantially in a shape of an inverted U with rounded corners, the strips having a portion of corresponding shape which is welded to the barrel along a contour of the inverted U shape. 
     
     
       4. The improvement according to claim 1, further comprising substantially frusto-conical sleeves fixing to the deflection plate the tubes which receive control rods and are integral with the deflection plate. 
     
     
       5. The improvement according to claim 1, wherein the deflection plate has a diameter of substantially four meters and a thickness of substantially 0.02 meter.